Nuro is right, they are quite suicidal fish and very sensitive from my experience. If you don't have a tight lid on your tank you can expect to find it on your floor at some time or another. I have read that they need space and it's not wise to put two together, but not impossible. If you do attempt this, do scatter rocks around, make sure the substrate is deep, and although I agree that it would be good to make sure the fish is healthy, if you want to add the second one you have to do it before the other completely claims the territory.